Is my data safe if one drive fails in RAID 5?

Yes. RAID 5 and single-parity SHR are designed to tolerate exactly one drive failure: when a drive dies, the array keeps serving your files from parity, and nothing is lost. But the safety margin is now spent, so what you do next matters.

You are protected, but exposed

After one failure the array is degraded: fully readable, zero remaining fault tolerance. If a second drive fails before you replace the first and complete the rebuild, the array crashes and the data is gone. The rebuild itself is a stress test on the surviving drives, which is when a marginal second drive is most likely to give out: the classic RAID 5 failure story.

What to do

1. Replace the failed drive promptly with a same-or-larger CMR drive.
2. Run Repair and let the rebuild finish before touching anything else.
3. Keep NAS load light during the rebuild.

Two bigger-picture points

• RAID is not a backup. It protects against drive failure, not deletion, ransomware, or a controller frying every drive. Keep a separate backup.
• For large arrays, prefer RAID 6 / SHR-2. With big drives the rebuild takes long enough that a second failure is a real risk; double parity survives it.

The table lists CMR NAS drives for the replacement.